| Shear flow is the typical flow phenomenon in work space of hydraulic components. It is widespread in the tiny gap with relative sliding, such as the flow of liquid in the tiny gap between motor port plate and cylinder and the flow in hydrostatic bearings or dynamic bearings etc. This phenomenon may cause the rupture of liquid film or cavitation and then lead to a series of issues such as wear, cavitation erosion, or even noise etc. In response to this practical problem, in this paper we have done some experiments on shear cavitation phenomenon in liquid through some new equipments. The main work I do is as follows:(1) The air content in liquid is the important factor that has great impact on shear cavitation, thus the measurement of air content in liquid is an important part for study shear cavitation. With a newly developed device and within a cetain range of temperature and pressure, experiments on air solubility for dimethyl silicone oil and hydraulic oil are carried out. After the data processing, the relationgship between Bunsen solubility and pressure and temperature was established. The results of data analysis showed that the linear relationship between Bunsen solubility and pressure is obvious and the Bunsen solubility of air is approximate the same for two dimethyl silicone oil samples with significant diferernt in molecular weight.(2) With the improved newly developed Couette rheometer, the experimental research on the influence of air content to shear cavitation inception is carried out. It proves that shear cavitation can occur in the supersaturated, saturated and less saturated dimethyl silicone oil. The relationship between the shear stress and pressure at shear cavitation inception is found. It is proved that it is feasible to judge shear cavitation inception according to temperature fluctuation in liquid. The equation between air saturation and Pecelt number, capillary number and cavitation index was established.(3) The experiments above was carried out with a nylon cylinder with a small gap of 0.3mm. With a new cylinder which is made from steel and has a wider gap (1mm), we carried on the shear cavitation experiment for silicone oil. Compare the experiment results and find it is difficult to find shear cavitation in the experiment with steel cylinder. Then we do some preliminary work to explain such phenomenon, and find there is no great difference in the wall features between the two cylinders. It is the difference in film thickness and thermal conductivity that results in the big difference in experiment.(4) As for viscoelastic liquid, normal stress and viscosity are important factors for shear cavitation. In this paper we fininsh the experiments on the viscoelastic liquid named Polydimethylsiloxane (PDMS) through a rotation rheometer. Deal with the experimental data with relative theories, and access to relax time, normal stress, shear stress and so on. At last the experiment on measurement of ari content in PDMS is carried out and the equation about press and Bunsen number and Moore concentration is established. Those are preparatory work for further study on shear cavitation of viscoelastic liquid. |
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